X-ray shield



P. MORRISON Dec. 25, i951 X-RAY SHIELD Filed Jan. 5l,

. INVENTOR. Plz zn Z 179 Morrison BY fwdm torne z/- Patented Dec. '25,Y1951 X-RAY SHIELD .Philip Morrison, Pittsburgh, Pa., assignor totheUnited States of America as represented by the 'United States AtomicEnergy Commission Application January 31, 194.5, .Serial No. .575,569

9 Claims. .(Cl. Z50-108) 4-My invention krelates to a shield that servesas `an efficient protection against X-rays, gamma rays and otherpenetrating radiations.

It is generally known that the heavier elements are more satisfactory asshields from X-rays,

gamma .rays and other` penetrating radiations,

than are the lighter elements, since the heavier elements can be used inthinner sections. Lead of suitable thickness has been usedY most widelyfor shielding operators and patients from the undesirable effects ofsuch penetrating radiations. For high radiation intensities ofpenetrating rays, such asobtained from a cyclotron target, radium, ornuclear ssion, appreciable thicknesses of lead are required,forrexample, of the order of several inches, making the shields veryexpensive, heavy and difficult to handle. Although uranium is a heavymetal, its use as a shield from X-rays, gamma rays and other penetratingradiations has been avoided in the past, because of an undesirablecharacteristic of uranium, the metal being itself an emitter of alphaand beta rays.

An object of my invention is to provide a shield that ishighly-efficient in preventing the transmission of X-rays, gamma raysand other penetratingradiations.

VAmore specific obj ect of my invention is to vnul-- lify theabove-mentioned undesirable characteristic of uranium, namely, its ownemission of alpha and beta rays, thus making uranium suitable as ashield for protection against X-rays, gamma rays and other penetratingradiations.

These and other objects will become more apparent from the followingdescription.

The effectiveness of a metallic shield for protection against X-rays, orgamma rays of energy greater than 2 m. e. v., that is, its absorptioncoeiiicient, is proportional to Where Z is the atomic number of theelement, P the density of the element and A the isotopic mass number ofthe element. The particular power of the factor Z is further dependentupon the particular X-ray energy and the absorption region. It can bedetermined mathematically that for two million electron volt radiations,corresponding to about 0.006 Angstrom, uranium is superior to lead as anabsorber of X-rays. More specifically, for two million electron volt (2m. e. v.) radiations, an equivalent shield of uranium is per centthinner than a tungsten shield, and 45 per cent less thick than a shieldof lead for the same absorption. Uranium is even more superior forradiations more penetrating,thatiagreater than enerf gies of 2 m. e. v.For frequencies somewhat less than the equivalent .of .2 m. e. v.radiation, uranium retains .an Vadvantage over lead lin Ashielding but:to a lesser vdegree in view .of .the ,applicationof the .expression forenergies in the neighborhood of 1 m. e. v., that is, theexpression'involves vthe first power of v'Z instead of Z2 asin the casefor energies of;2'm.. e.v. andabove.

Inasmuch as uranium is itself an emitter of alpha and beta rays, its useas a shield for X-rays and the like has not'hitherto been considered.

have found, however, that the above-mentioned disadvantage can berovercome `by coating the yuranium metal with a heavymetal pigment, suchas, for example, red lead. This pigment coating effectively absorbs boththe alpha and be'ta vradiations from the uranium. Thus, the combinationof a surface coating of lead lwith a thick uranium absorber possessesoutstanding advantages in the control of penetratingradiations such asX-rays andgamrna rays as Well as alphamore eicient than lead 'forradiation ireguencies.

corresponding, for example, to two million electron Volts (2 m. e. v.)energy, or more. Furthermore, I have eliminated the inherentdisadvantage of uranium used as a shield material, because of its ownemission of alpha and beta rays, by coating the uranium with a materialthat absorbs these self-generated radiations, such as, for example,lead.

For an illustration of an embodiment of the invention in accordance withthe patent laws, reference is made to the attached drawing in which:

Figure l is a schematic plan View of a shield Wall made in accordancewith the invention together with a radiation source; and

Figure 2 is a fragmentary cross-sectional view of the shield wall ofFigure 1.

As illustrated in Figure 1, the shield wall 4 is employed to absorb andshield the radiations emanating from an X-ray or gamma ray source 6. Asshown in Figure 2, the wall 4 consists of a sheet 8 of uranium, on theouter surface of which is a relatively thin layer I0 of another heavymaterial. such as lead in the form of a red-lead pigment.

It should be noted that the above-described embodiment of the use ofuranium as a shield is merely illustrative and not limiting, insofar asmy invention is concerned. Other modification will be readily suggestedto those skilled in the art after having had the benefit of theteachings of my invention. YFor example, instead of using uranium metalas a shield, an alloy, or perhaps a compound, containing a largepercentage of uranium, may be used instead. Furthermore, instead ofpainting the uranium surface with a heavy metal pigment, such as redlead, a thin sheet of. lead or other suitable absorbing material such asbismuth, may be used as a` 'surface sheet either adjacent to orseparated from the uranium', for the purpose of absorbing alpha and betarays. In short, any material having Ia relatively high absorptioncoeiiicient for alpha and beta rays may be used. For these reasons, myinvention shouldvnot be limited except insofar as set forth in thefollowing claims.

I claim:

1.fA shield for substantially preventing the transmission of X-rays,gamma rays and other penetrating radiations, comprising a uranium metalbase and a coating of heavy metal on said base, said coating consistingof non-radioactive elements of a density at least equal to that of redlead.

2. A shield for substantially preventing the transmission of X-rays,gamma rays and other penetrating radiations, comprising a uraniumcontaining base and a coating of heavy metal pigment on said base,said'coating consisting of nonradioactive elements of a density at leastequal to that of red lead.

3. VA shield for substantially preventing the transmission of X-rays,gamma rays and other penetrating radiations comprising a sheet ofuraniumtogether with a surface sheet of lead.

4. Al shield for substantially preventing the transmission of X-rays,gamma rays and other penetrating radiations comprising a sheet ofuranium and a sheet of material having an absorption coeiicient foralpha and beta rays at least equal to that of red lead, said materialconsisting of non-radioactive elements.

5. A shield for substantially preventing the transmission of X-rays,gamma rays and other penetrating radiations, comprising a sheet of ura-Vnium and a red lead pigment coated on the sur- 'face of said sheet.

6. In combination with a source for producing penetrating radiations,such as X-rays and gamma rays, a protective shield for absorbing saidrays and preventing transmission thereof through said shield comprisinga sheet of uranium together with a sheet of material having a relativelyhigh absorption coefficient for alpha and beta rays emitted by saiduranium sheet said material consisting of non-radioactive elements of adensity at least equal to that of red lead.

7. In combination with a source for producing penetrating radiations,such as X-rays and gam.. ma rays, a protective shield for absorbing saidrays and preventing transmission thereof through Said shield, comprisinga sheet of uranium together with a sheet of heavy non-radioactive metalhaving an absorption coefficient for alpha and beta rays at least equalto that of red lead, said last-named sheet being furthermost from saidsource. v

8. In combination with a source for producing penetrating radiations,such as X-rays, and gamma rays, a protective shield for absorbing saidrays and preventing transmission thereof through said shield, comprisinga sheet of uranium and a coating of heavy non-radioactive metal pigmentof a density at least equal to that of red lead on the surface of saiduranium sheet to absorb alpha and beta rays emitted by said uraniumsheet.

9. In combination With a source for producing penetrating radiations,such as X-rays and gamma rays, a protective shield for absorbing saidrays and preventing transmission thereof through said shield comprisinga sheet of uranium and a coating of red lead on the surface of saiduranium sheet to absorb alpha and beta rays emitted by said uraniumsheet.

PHILIP MORRISON.

REFERENCES lCITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,815,922 Lapof July 28, 19311,902,474 Ungelenk Mar. 21, 1933 1,918,996 Weger July 18, 1933 2,183,799Dillehay et al. Dec. 19, 1939

1. A SHIELD FOR SUBSTANTIALLY PREVENTING THE TRANSMISSION OF X-RAYS,GAMMA RAYS AND OTHER PENETRATING RADIATIONS, COMPRISING A URANIUM METALBASE AND A COATING OF HEAVY METAL ON SAID BASE, SAID COATING CONSISTINGOF NON-RADIOACTIVE ELEMENTS OF A DENSITY AT LEAST EQUAL TO THAT OF REDLEAD.